zillion

UK: /ˈzɪljən/ US: /ˈzɪljən/ ,(zil′yən)

Inflections of 'zillion' (n):

zillions

npl (Used without a preceding number—e.g. "Lucy could see zillions of stars in the sky.")

zillion

npl (Used with a preceding number—e.g. "The cost is estimated at $4 zillion.")

WordReference Random House Learner's Dictionary of American English © 2025

zil•lion /ˈzɪlyən/   n. [countable] , pl. -lions, (as after a numeral) -lion. [Informal.]

1. Informal Terms an extremely large number or amount that is not made definite:
   a zillion thanks.

WordReference Random House Unabridged Dictionary of American English © 2025

zil•lion  (zil′yən), n., pl. -lions, (as after a numeral) -lion, adj. [Informal.]
n. 

1. Informal Terms an extremely large, indeterminate number.

adj. 

2. Informal Terms of, pertaining to, or amounting to a zillion.

• jocular alteration of million, billion, etc. 1930–35

Collins Concise English Dictionary © HarperCollins Publishers::

zillion / ˈzɪljən/ noun ( -lions, -lion)

1. (often plural) an extremely large but unspecified number, quantity, or amount: zillions of flies in this camp

determiner

1. amounting to a zillion: a zillion different problems

Etymology: 20th Century: on the model of million